CHAPTER 14

Mirrors and Lenses

• Mirrors have a highly reflective surface. Mirrors work by• Light striking the mirror and being reflected back.

• The reflected waves hit an object facing the mirror, illuminating the object.

• The waves of light enter your eyes.

• Your brain interprets the rays at the point the rays come together, which allows your brain to form an image (virtual image.)

• The virtual image formed by a plane (flat) mirror is always upright and appears to be far behind the mirror as the object is to the front of it.

Mirrors

• Think of the front wedge of a spoon. The curves on this part of the spoon is similar to the curves you would find in a concave mirror.

• When the light waves hit the mirror, the light waves reflected converge (come together) to a focal point. Your brain will think the light waves reflected off of the mirror come from a point behind the mirror. In reality, the real (virtual) image is in front of the mirror.

Concave Mirrors

• Think of the back of a spoon, here the center curves outward. Convex mirrors allow you to see larger areas, but they are not real images. Security and rearview mirrors are convex mirrors.

• Unlike concave, convex mirrors diverge. They don’t come together. The image formed is actually smaller than a real image. You can see further, but the objects appear smaller and further away than they really are.

Convex Mirrors

Lenses

• A lens is a transparent material with at least one curved surface that causes light rays to bend (refract) as they pass through.

• Like mirrors, lenses can be concave or convex.

• Lenses are often used to correct vision. Since the image is formed behind the retina, concave and convex lenses correct the way the light comes into the eye.

• A wide angle lens produces a small image that includes much of the surroundings.

• A concave lens is thinner in the middle and thicker at the edges.

• Concave lenses help with nearsightedness (nearby objects are clearer than objects at a distance.) Concave lenses cause light to diverge before they enter the eye, allowing the person to see more light from a distant object.

• They are also used in combination with other lenses to enhance light at a focal point.

Concave Lenses

• A convex lens is thicker in the middle than around the edges.

• Convex lenses bends light rays so they don’t spread out as much. They produce a small image that includes much of the surroundings.

• Convex lenses help with farsightedness (people who can see distant objects better than objects up close.)

Convex Lenses

A telescope uses lenses and concave mirrors to increase the light coming in from distant places, so that your eye can receive that light and your brain interpret the information.

Refracting Telescope - A simple telescope, it uses 2 convex lenses to magnify the light.

Reflecting Telescope – A more complex telescope that can enhance light from distant places. It uses a concave mirror, a plane (flat) mirror and a convex lens to converge light at a focal point.

Telescopes